This invention relates to an improved refrigeration system for cooling a water supply to be circulated through or around industrial equipment and other similar equipment, and particularly to a system which includes a subcooling condenser.
Water chillers are useful for cooling a circulating water supply for use in maintaining industrial equipment at desired operating temperatures. Such equipment may take the form of machines for blow molding, injection molding, extruding, printing and etching, chemical processing, food processing, and the like. It has been found, for example, that the use of water chillers with industrial machines such as hydraulic presses, compressors, metal treating ovens, and special metal fabrication processes results in definite improvements in operating efficiency. However, water chillers used in the past have often taken the form of large and complex refrigeration systems operating at high energy levels and, even then, oftentimes failing to achieve a satisfactory temperature drop in a circulating water supply when ambient temperatures are excessive.
With respect to prior water chillers, such refrigeration systems have usually been of conventional designs. The coiled refrigerant tubes or evaporators are simply immersed in a container of water to chill the water used for cooling the industrial equipment. Even when such a chiller is used, however, ambient temperatures often reach high levels and greatly reduce the water cooling capacity of the system. For example, it has been found that a typical refrigerant compressor loses between 6 and 10% cooling capacity for each 10.degree. F. of ambient temperature which exceeds 95.degree. F. There has therefore developed a need to somehow increase refrigeration capacity when relatively high ambient temperatures impede the efficiency of such a compresser.
Several methods have been suggested in the art for increasing the refrigeration capacity of a chiller, such as by increasing compressor capacity or the volume of refrigerant used in the system. Other methods known in the art include bringing the refrigerant gas, downstream from the evaporator, into a heat exchange relationship with condensed refrigerant leaving the condenser. Systems which cool refrigerant leaving a condenser are known in the art, it being recognized that cooling condensed refrigerant at a high temperature, for example 125.degree. F., is easier to accomplish than cooling refrigerant at a relatively low temperature, for example -40.degree. F. One prior system for subcooling condense refrigerant is exemplied in U.S. Pat. No. 3,582,974 which teaches the use of a secondary refrigeration system. In such a system, a secondary refrigerant circuit includes evaporator coils in heat transfer relationship with a primary refrigerant circuit so as to subcool the condensed refrigerant of the primary circuit before the refrigerant reaches an expansion valve. Although such a system increases the efficiency of the primary refrigeration system by subcooling the condensed refrigerant, such increases in efficiency tend to be largely offset by the cost and complexity of providing a secondary refrigeration system.
In the system of the present invention, refrigerant leaving the condenser may be subcooled to increase the refrigerating capacity of the system. A coiled subcooling condenser tube is disposed in the body of water to be cooled by the system. When ambient temperatures exceed a predetermined level, the flow of condensed refrigerant through a first circuit which leads directly to the expansion valve of the evaporator coil is re-routed through a second circuit which includes the subcooling condenser coil immersed in the body of water. Refrigerant flowing through the subcooling condenser at high temperature, for example at 125.degree. F., is subcooled by the chilled body of water in the container which is at a relatively low temperature, for example, at 40.degree. F. The cooled refrigerant then flows through the expansion valve at a relatively low temperature, resulting in a lower refrigerant temperature in the evaporator and thereby increasing the refrigerating capacity of the system to compensate for the decreased capacity of the compressor.
In a preferred embodiment, the heat exchange between the coiled water tubes and the associated refrigerant passages takes the form of at least one coiled refrigerant-conducting tube which contains a plurality of smaller water tubes having outer surfaces that are threaded, or provided with generally circumferentially-extending ribs, and having longitudinally-extending channels along their outer surfaces. The refrigerant-conducting tube and water-conducting tubes therein are formed of metal having relatively high thermal conductivity and that, combined with the relatively large inside diameter of the refrigerant-conducting tube and the substantial surface area of the water tubes therein, provides an arrangement that promotes high thermal transfer efficiency in the refrigeration system.
Other features, advantages, and objects of the invention will become apparent from the specification and drawings.